DEVELOPMENT OF DIAGNOSIS PROCEDURE OF MATERIALS DEGRADATION BY MEANS OF NONDESTRUCTIVE ELECTROCHEMICAL TECHNIQUE FOR REMAINING LIFE PREDICTION

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A NEW EVALUATION PROCEDURE FOR DETECTION AND DIAGNOSIS OF MATERIALS DEGRADATION OF HEAT RESISTANT MATERIALS WAS DEVELOPED WHICH HAS BEEN REQUIRED TO BE DEVELOPED FOR ENSURING THE STRUCTURAL SAFETY AND INTEGRITY OF COMPONENTS USED FOR A LONG TERM IN SERVICE. THE BASIC MECHANISMS OF DAMAGE DETECTION IS APPLICATION OF ELECTROCHEMICAL TECHNIQUE SUCH AS ANODIC POLARIZATION MEASUREMENTS AND IMPEDANCE SPECTROSCOPY MEASUREMENT FOR EVALUATION OF MICROSTRUCTURAL CHANGES CAUSED DURING THE SERVICE TIME AT ELEVATED TEMPERATURE. THE MATERIALS USED IN THIS INVESTIGATION ARE AUSTENITIC STAINLESS STEELS, Cr-Mo-V STEELS AND Cr-Mo STEELS WHICH ARE COMMONLY USED AS BOILER SUPERHEATER, TURBINE ROTORS AND CASING, REACTOR OF CHEMICALPLANTS AND BOILER HEADER. THE RESULTS CAN BE SUMMARIZED AS FOLLOWS, 1. EMBRITTLEMENT AND REDUCTION OF CREEP RESISTANCE OF SUS 321 and 316 DUE TO SIGMA PHASE FORMATION AND CARBIDE PRECIPITATION CAN BE DETECTED BY POLARIZATION MEASUREMENT IN KOH SOLUTION. 2. A SOLUTION FOR DETECTION OF TEMPER EMBRITTLEMENT OF Cr- Mo- V STEELS IS DEVELOPED WITH A VERY HIGH SENSITIVITY RATHER THAN PICRIC ACID SOLUTION. 3. A DETECTION SOLUTION WAS DEVELOPED FOR SELECTIVE DETECTION OF M6C CARBIDES WHICH CAUSE THE VARIOUS DETERIORATION SUCH AS SOFTNING, CARBIDE EMBRITTLEMENT ETC. 4. DEVELOPMENT OF GELL ELECTRODE, SMALL ELECTOCHEMICAL CELL AND HANDY TYPE POTENTIOSTATT WERE ACHIEVED FOR THE IN-SITU MEASUREMENTS AT THE PLANTS. 5. DEVELOPMENT OF DATA BASE FOR THE SYSTEMATIC PROCEDURE TO DETECT THE VARIOUS TYPE OF DEGRADATION AND THEIR STANDARIZATION.